Gallery2: Fix force closed when input long size at Export Flattened Image.

If input long size, the NumberFormatException occur
when parse int from string.

Try to catch the NumberFormatException,
and use the original width and height for user.

Change-Id: I5401f400c2ddb79aa9bd952a02de1c45222f5ae0
CRs-Fixed: 1002767